The public show of togetherness in College Station, Tex., provided a stark contrast to recent speeches by George W. Bush and Mr. Obama, who appeared to criticize Mr. Trump without explicitly referring to him.
Their remarks garnered attention in part because Mr. Bush and Mr. Obama have maintained relatively low profiles after leaving office and have largely avoided speaking out against Mr. Trump since he was inaugurated in January.
For a few hours on Saturday, however, all six leaders seemed to put aside their differences to help the hurricane victims.
Several of the former presidents waved from the stage as an American flag flashed on the screen behind them, taking their seats after the national anthem.
Soon after Mr. Trump’s video was played, the former presidents joined the stage again. In brief remarks, Mr. Carter and Mr. Clinton praised Americans’ volunteerism. Mr. Obama thanked both members of the Bush family, who live in Texas, and spoke about the important work of citizens.
“Americans step up,” Mr. Obama said. “And as heartbreaking as the tragedies that took place here in Texas, and in Florida, in Puerto Rico and the U.S. Virgin Islands have been, what we’ve also seen is the spirit of America at its best.”
George W. Bush spoke last, urging viewers to donate and honoring his father.
“We really admire and love George H. W. Bush,” he said before standing behind his father, who remained seated. The former presidents then received a loud standing ovation.
Video by One America Appeal
The presidents have a history of coming together after natural disasters.
Mr. Clinton teamed up with the elder Mr. Bush to raise money after Hurricane Katrina struck the Gulf Coast in 2005. When he was commander in chief, Mr. Obama asked Mr. Clinton and George W. Bush to lead an effort to help Haiti after an earthquake in 2010.
Donations to the current campaign, One America Appeal, will help victims of Hurricane Harvey in Texas, Hurricane Irma in Florida and Hurricane Maria in Puerto Rico and the United States Virgin Islands, according to the campaign’s website. It has raised more than $31 million, officials announced on Saturday.